Numerous disorders affecting the spinal column and in particular affecting the intervertebral discs are currently known in medicine.
Some of these disorders produce a degeneration of the fibrous capsule of the intervertebral disc, which reduces its elasticity and becomes damaged, allowing part of the nucleus pulposus to escape.
This phenomenon is commonly known as “hernia”.
There are also other disorders, of a progressive type, which entail the thinning, over time, of the intervertebral disc owing to the loss of its ability to retain water inside it. This thinning often also produces the thinning of the facet capsules, with consequent pain.
In some cases, this thinning can lead to the reduction of the medullary canal, with a severe risk of chronic claudication.
In many cases, progressive deterioration of the intervertebral disc requires the implantation of an intervertebral prosthesis, which substantially replaces said disc.
Among the various known types of intervertebral prosthesis, one is available which has the main function of facilitating the fusion of two adjacent vertebrae.
This type of prosthesis generally comprises one or two bodies made of osteoconductive material which are arranged, by way of a surgical procedure, in mutually opposite positions between the two adjacent vertebrae.
The materials used to provide the two bodies facilitate the growth and adhesion of bone tissue so as to cause the fusion of the two vertebrae, which can no longer move with respect to each other.
This type of conventional intervertebral prosthesis, which is generally applied at the level of the lumbar vertebrae, which are the ones subjected to the greatest load determined by body weight, is not free from drawbacks, which include the fact that generally it requires an extremely invasive surgical procedure for implantation.
The surgeon in fact proceeds by preparing the intervertebral disc to accommodate the intervertebral prosthesis and inserts the prosthesis itself by creating initially a percutaneous anterolateral access of such size as to be able to accommodate a cylindrical retractor instrument, which, once inserted in the patient through said percutaneous anterolateral access, affords a maneuvering channel that is of width comprised generally between six and nine centimeters, is delimited laterally by the retractor instrument, and is fully free from the organic tissues that are present between the access created and the intervertebral disc to be operated on.
In this manner, the surgeon can operate on the disc by working visually and by inserting the various surgical instruments, as well as the prosthesis itself, through the maneuvering channel that has been created.
In greater detail, the method described above involves entry with a first small cylindrical instrument, then cannulas that have the function of expanding the first access, and finally the retractor, which also expands further the first access.
It should be stressed that this surgical procedure, in addition to being inherently laborious and time-consuming, can lead to severe consequences for the patient since, although the procedure is monitored at the neurological level by a device that detects if there is a nervous structure proximate to the surgical instrument, it does not allow the surgeon to detect and therefore monitor the compression of tissues and muscles (against the transverse apophyses) caused by the divarication or expansion of the retractor instrument, which very often leads to the stretching and/or compression of the femoral plexus throughout the duration of the procedure.
This can sometimes lead to temporary dysesthesias of the associated femoral nerve and to paresthesias, motor deficits of the quadriceps, weakness in hip flexion, and in some cases to actual permanent damage of the plexus itself, all the consequences cited above being permanent.
Indeed, recently manufacturers have recommended closing the retractor every ten minutes and waiting another ten minutes before resuming the procedure.
Another drawback of the background art, discussed in some studies, consists in that in a lateral position at the L4-L5 and L3-L4 level the veins and aortas approach the space affected by the procedure.
A further drawback of the background art consists in that it requires the removal also of a portion of annulus that is as wide as the implant that will be positioned in addition to the internal part of the disc (nucleus pulposus), which leads to an incorrect placement of the implant in said disc.
A further drawback of the background art consists in the onset, a short time later, of inguinal hernias caused by the access (tissue stress).
A further drawback of the background art consists in that, if it is necessary to remove the implant owing to infections, incorrect placement or size, et cetera, then surgery to remove and/or replace the implant is highly invasive and complex.
A further drawback of the background art consists in that, if it is necessary to provide posterior stabilization (70% of cases), with the background art first of all lateral access is provided in order to position the implant and then the patient is turned over to perform the arthrodesis procedure via a posterior pathway; this entails removing all the surgical sheets from the patient, repositioning him/her on the operating table, placing the new sheets again with the posterior access and continuing with the procedure. If efficient operating room staff is available, this procedure requires 25 minutes, extending all operating times (anesthesia, etc.).